FROM THE FLUE OF A FURNACE. 295 



is only necessary to sprinkle some of this material on an 

 inclined glass plate, and by gentle vibration tbe balls roll 

 down and can thus be collected. Having satisfied our- 

 selves with the examination under the microscope, it is 

 natural that we should desire to know more about these 

 novel objects. What is their elementary constitution? 

 Why are they spherical ? How do they get into the flue ? 

 I have not attempted a chemical analysis of these minute 

 bodies, many of which are less than the looth part of an 

 inch in diameter. I can only therefore offer an opinion 

 as to their probable constitution, judging from what is 

 known of the chemical analysis of coal-ash, and from the 

 appearance they present under the microscope. Eeferring 

 to the chemical analysis of coal-ash, we find that it some- 

 times contains silica, magnesia, alumina, sesquioxide of 

 iron, lime, soda, potash, sulphate of calcium, anhydrous 

 sulphuric acid, anhydrous phosphoric acid, sulphur, and 

 sometimes traces of copper and lead. The vegetable origin 

 of coal is now generally admitted ; and doubtless some of 

 the substances I have just named have been taken up by 

 the coal-plants, whilst other portions may have collected 

 in the locality where the coal was formed. As this is not 

 immediately connected with our present inquiry, I proceed 

 to speculate as to the constitution of these globular bodies. 

 The transparent spheres I imagine to be silicates of soda 

 or potash ; the opaque white are niost likely silicate of 

 soda or potash combined with lime and alumina ; the yellow 

 and brown are silicates coloured by iron in different pro- 

 portions. The black globes are not all alike in composi- 

 tion ; some of these are silicates coloured by carbon, others 

 are iron balls coated externally with a silicate. Many of 

 these rusty cannon-balls are probably ferrous oxide formed 

 by the action of heat on the iron-pyrites in the coal. 

 There are also balls of black magnetic oxide : the perfor- 

 ated shells are probably ferrous sulphides. The globular 



